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1.
Photosynthetic electron transfer has been examined in whole cells, isolated membranes and in partially purified reaction centers
(RCs) of Roseicyclus mahoneyensis, strain ML6 and Porphyrobacter meromictius, strain ML31, two species of obligate aerobic anoxygenic phototrophic bacteria. Photochemical activity in strain ML31 was
observed aerobically, but the photosynthetic apparatus was not functional under anaerobic conditions. In strain ML6 low levels
of photochemistry were measured anaerobically, possibly due to incomplete reduction of the primary electron acceptor (QA) prior to light excitation, however, electron transfer occurred optimally under low oxygen conditions. Photoinduced electron
transfer involves a soluble cytochrome c in both strains, and an additional reaction center (RC)-bound cytochrome c in ML6. The redox properties of the primary electron donor (P) and QA of ML31 are similar to those previously determined for other aerobic phototrophs, with midpoint redox potentials of +463 mV
and −25 mV, respectively. Strain ML6 showed a very narrow range of ambient redox potentials appropriate for photosynthesis,
with midpoint redox potentials of +415 mV for P and +94 mV for QA. Cytoplasm soluble and photosynthetic complex bound cytochromes were characterized in terms of apparent molecular mass. Fluorescence
excitation spectra revealed that abundant carotenoids not intimately associated with the RC are not involved in photosynthetic
energy conservation. 相似文献
2.
Analysis of EF-hand-containing proteins in <Emphasis Type="Italic">Arabidopsis</Emphasis> 总被引:3,自引:0,他引:3
Background
In plants, calcium (Ca2+) has emerged as an important messenger mediating the action of many hormonal and environmental signals, including biotic and abiotic stresses. Many different signals raise cytosolic calcium concentration ([Ca2+]cyt), which in turn is thought to regulate cellular and developmental processes via Ca2+-binding proteins. Three out of the four classes of Ca2+-binding proteins in plants contain Ca2+-binding EF-hand motif(s). This motif is a conserved helix-loop-helix structure that can bind a single Ca2+ ion. To identify all EF-hand-containing proteins in Arabidopsis, we analyzed its completed genome sequence for genes encoding EF-hand-containing proteins. 相似文献3.
Schaloske RH Lusche DF Bezares-Roder K Happle K Malchow D Schlatterer C 《BMC cell biology》2005,6(1):13
Background
Stimulation of Dictyostelium discoideum with cAMP evokes an elevation of the cytosolic free Ca2+ concentration ([Ca2+]i). The [Ca2+]i-change is composed of liberation of stored Ca2+ and extracellular Ca2+-entry. The significance of the [Ca2+]i-transient for chemotaxis is under debate. Abolition of chemotactic orientation and migration by Ca2+-buffers in the cytosol indicates that a [Ca2+]i-increase is required for chemotaxis. Yet, the iplA - mutant disrupted in a gene bearing similarity to IP3-receptors of higher eukaryotes aggregates despite the absence of a cAMP-induced [Ca2+]i-transient which favours the view that [Ca2+]i-changes are insignificant for chemotaxis. 相似文献4.
Effects of intracellular Mg2+ on a native Ca2+-and voltage-sensitive large-conductance K+ channel in cultured human renal proximal tubule cells were examined with the patch-clamp technique in the inside-out mode.
At an intracellular concentration of Ca2+ ([Ca2+]i) of 10−5–10−4 M, addition of 1–10 mM Mg2+ increased the open probability (Po) of the channel, which shifted the Po –membrane potential (Vm) relationship to the negative voltage direction without causing an appreciable change in the gating charge (Boltzmann constant).
However, the Mg2+-induced increase in Po was suppressed at a relatively low [Ca2+]i (10−5.5–10−6 M). Dwell-time histograms have revealed that addition of Mg2+ mainly increased Po by extending open times at 10−5 M Ca2+ and extending both open and closed times simultaneously at 10−5.5 M Ca2+. Since our data showed that raising the [Ca2+]i from 10−5 to 10−4 M increased Po mainly by shortening the closed time, extension of the closed time at 10−5.5 M Ca2+ would result from the Mg2+-inhibited Ca2+-dependent activation. At a constant Vm, adding Mg2+ enhanced the sigmoidicity of the Po–[Ca2+]i relationship with an increase in the Hill coefficient. These results suggest that the major action of Mg2+ on this channel is to elevate Po by lengthening the open time, while extension of the closed time at a relatively low [Ca2+]i results from a lowering of the sensitivity to Ca2+ of the channel by Mg2+, which causes the increase in the Hill coefficient.
M. Kubokawa and Y. Sohma contributed equally to this work. 相似文献
5.
M. P. Fernandes N. M. Inada M. R. Chiaratti F. F. B. Araújo F. V. Meirelles M. T. S. Correia L. C. B. B. Coelho M. J. M. Alves F. R. Gadelha A. E. Vercesi 《Journal of bioenergetics and biomembranes》2010,42(1):69-78
Incubation of T. cruzi epimastigotes with the lectin Cramoll 1,4 in Ca2+ containing medium led to agglutination and inhibition of cell proliferation. The lectin (50 μg/ml) induced plasma membrane
permeabilization followed by Ca2+ influx and mitochondrial Ca2+ accumulation, a result that resembles the classical effect of digitonin. Cramoll 1,4 stimulated (five-fold) mitochondrial
reactive oxygen species (ROS) production, significantly decreased the electrical mitochondrial membrane potential (ΔΨm) and impaired ADP phosphorylation. The rate of uncoupled respiration in epimastigotes was not affected by Cramoll 1,4 plus
Ca2+ treatment, but oligomycin-induced resting respiration was 65% higher in treated cells than in controls. Experiments using
T. cruzi mitochondrial fractions showed that, in contrast to digitonin, the lectin significantly decreased ΔΨm by a mechanism sensitive to EGTA. In agreement with the results showing plasma membrane permeabilization and impairment of
oxidative phosphorylation by the lectin, fluorescence microscopy experiments using propidium iodide revealed that Cramoll
1,4 induced epimastigotes death by necrosis. 相似文献
6.
Gametophores of mosses Mnium undulatum and Polytrichum commune were submerged in distilled water or in calcium chloride solution (0.9 mM Ca2+) to induce hypoxia. The net photosynthetic (PN) and dark respiration rate (RD) were measured in the air containing 300–400 μmol(CO2)·mol−1(air) and 0.21 mol(O2)·mol−1(air). PN of M. undulatum gametophores decreased to 58 % of the control after 1-h submersion in water, whereas to 80 % of the control in P. commune gametophores. A smaller decrease in PN was observed when the gametophores were immersed in CaCl2 solution. In hypoxia, RD in the tested mosses species was a little higher than in the control. 相似文献
7.
Toshiyuki Kaneko Naoya Takahashi Munehiro Kikuyama 《The Journal of membrane biology》2009,228(1):33-42
In order to confirm that mechanosensitive Ca2+ channels are activated by membrane stretching, we stretched or compressed the plasma membrane of Chara by applying osmotic shrinkage or swelling of the cell by varying the osmotic potential of the bathing medium. Aequorin studies
revealed that treatments causing membrane stretching induced a transient but large increase in cytoplasmic concentration of
Ca2+ (Δ[Ca2+]c). However, the observed Δ[Ca2+]c decreased during the treatments, resulting in membrane compression. A second experiment was carried out to study the relationship
between changes in membrane potential (ΔE
m) and stretching or compression of the plasma membrane. Significant ΔE
m values, often accompanied by an action potential, were observed during the initial exchange of the bathing medium from a
hypotonic medium to a hypertonic one (plasmolysis). ΔE
m appears to be triggered by a partial stretching of the membrane as it was peeled from the cell wall. After plasmolysis, other
exchanges from hypertonic to hypotonic media, with their accompanying membrane stretching, always induced large ΔE
m values and were often accompanied by an action potential. By contrast, action potentials were scarcely observed during other
exchanges from hypotonic to hypertonic solutions (=membrane compression). Thus, we concluded that activation of the mechanosensitive
channels is triggered by membrane stretching in Chara. 相似文献
8.
Jin Zhou Ju Chu Yong-Hong Wang Si-Liang Zhang Ying-Ping Zhuang Zhong-Yi Yuan 《World journal of microbiology & biotechnology》2008,24(6):789-796
An intracellular S-adenosylmethionine synthetase (SAM-s) was purified from the fermentation broth of Pichia pastoris GS115 by a sequence chromatography column. It was purified to apparent homogeneity by (NH4)2SO4 fractionation (30–60%), anion exchange, hydrophobic interaction, anion exchange and gel filtration chromatography. HPLC showed
the purity of purified SAM-s was 91.2%. The enzyme was purified up to 49.5-fold with a final yield of 20.3%. The molecular
weight of the homogeneous enzyme was 43.6 KDa, as determined by electro-spray ionization mass spectrometry (ESI-MS). Its isoelectric
point was approximately 4.7, indicating an acidic character. The optimum pH and temperature for the enzyme reaction were 8.5
and 35 °C, respectively. The enzyme was stable at pH 7.0–9.0 and was easy to inactivate in acid solution (pH ≤ 5.0). The temperature
stability was up to 45 °C. Metal ions, such as, Mn2+ and K+ at the concentration of 5 mM had a slight activation effect on the enzyme activity and the Mg2+ activated the enzyme significantly. The enzyme activity was strongly inhibited by heavy metal ions (Cu2+ and Ag2+) and EDTA. The purified enzyme from the transformed Pichia pastoris synthesized S-adenosylmethionine (SAM) from ATP and l-methionine in vitro with a K
m of 120 and 330 μM and V
max of 8.1 and 23.2 μmol/mg/min for l-methionine and ATP, respectively. 相似文献
9.
Supplementation with CaCl2·2H2O (50 mg l−1) or CuSO4·5H2O (10 mg l−1) improved mannitol production by Candida magnoliae by 14.5 and 18.6% (25 and 32 g/L), respectively. When used in combination, they acted synergistically: Ca2+ decreased the intracellular concentration of mannitol 30%, whereas Cu2+ increased the intracellular activity of mannitol dehydrogenase 1.6-times more than control. Ca2+ probably works by altering the permeability of cells to mannitol, whereas, Cu2+ increases the activity of an enzyme responsible for mannitol biosynthesis. 相似文献
10.
Qingxin Zhao Sheng Yuan Yuling Zhang Hong Zhu Chuanchao Dai Fang Yang Fengmin Han 《World journal of microbiology & biotechnology》2007,23(8):1057-1064
Pectate lyase A (PelA) of Aspergillus nidulans was successfully expressed in Escherichia coli and effectively purified using a Ni2+-nitrilotriacetate-agarose column. Enzyme activity of the recombinant PelA could reach 360 U ml−1 medium. The expressed PelA exhibited its optimum level of activity over the range of pH 7.5–10 at 50°C. Mn2+, Ca2+, Fe2+, Mg2+ and Fe3+ ions stimulated the pectate lyase activity, but Cu2+ and Zn2+ inhibited it. The recombinant PelA had a V
max of 77 μmol min−1 mg−1 and an apparent K
m of 0.50 mg ml−1 for polygalacturonic acid. Low-esterified pectin was the optimum substrate for the PelA, whereas higher-esterified pectin
was hardly cleaved by it. PelA efficiently macerated mung bean hypocotyls and potato tuber tissues into single cells. 相似文献
11.
Aporn Bualuang Kanteera Soontharapirakkul Aran Incharoensakdi 《Journal of applied phycology》2010,22(2):123-129
The activity of Na+/H+ exchanger to remove toxic Na+ is important for growth of organisms under high salinity. In this study, the halotolerant cyanobacterium Aphanothece halophytica was shown to possess Na+/H+ exchange activity since exogenously added Na+ could dissipate a pre-formed pH gradient, and decrease extracellular pH. Kinetic analysis yielded apparent K
m (Na+) and V
max of 20.7 ± 3.1 mM and 3,333 ± 370 nmol H+ min−1 mg−1, respectively. For cells grown under salt-stress condition, the apparent K
m (Na+) and V
max was 18.3 ± 3.5 mM and 3,703 ± 350 nmol H+ min−1 mg−1, respectively. Three cations with decreasing efficiency namely Li+, Ca2+, and K+ were also able to dissipate pH gradient. Only marginal exchange activity was observed for Mg2+. The exchange activity was strongly inhibited by Na+-gradient dissipators, monensin, and sodium ionophore as well as by CCCP, a protonophore. A. halophytica showed high Na+/H+ exchange activity at neutral and alkaline pH up to pH 10. Cells grown at pH 7.6 under high salinity exhibited higher Na+/H+ exchange activity than those grown under low salinity during 15 days of growth suggesting a role of Na+/H+ exchanger for salt tolerance in A. halophytica. Cells grown at alkaline pH of 9.0 also exhibited a progressive increase of Na+/H+ exchange activity during 15 days of growth. 相似文献
12.
Elicitation can lead to overproduction of secondary metabolites in plants and microbes. Potential changes in cytosolic Ca2+ levels in bacteria were studied in response to elicitation. We report, for the first time, the effect of oligosaccharide
elicitors on intracellular Ca2+ levels. The apoaequorin gene was cloned into Escherichia coli DH5α and Bacillus subtilis 1604 cultures. Addition of elicitors, oligoguluronate and mannan oligosaccharides, to the cultures caused up to 11-fold increase
in cytosolic Ca2+ in E. coli and tenfold increase in B. subtilis. These increases in Ca2+ levels could therefore contribute to the enhancement of secondary metabolite levels. 相似文献
13.
Although resistance of microorganisms to Hg(II) salts has been widely investigated and resistant strains have been reported
from many eubacterial genera, there are few reports of mercuric ion resistance in extremophilic microorganisms. Moderately
thermophilic mercury resistant bacteria were selected by growth at 62 °C on Luria agar containing HgCl2. Sequence analysis of 16S rRNA genes of two isolates showed the closest matches to be with Bacillus pallidus and Ureibacillus thermosphaericus. Minimum inhibitory concentration (MIC) values for HgCl2 were 80 μg/ml and 30 μg/ml for these isolates, respectively, compared to 10 μg/ml for B. pallidus H12 DSM3670, a mercury-sensitive control. The best-characterised mercury-resistant Bacillus strain, B. cereus RC607, had an MIC of 60 μg/ml. The new isolates had negligible mercuric reductase activity but removed Hg from the medium
by the formation of a black precipitate, identified as HgS by X-ray powder diffraction analysis. No volatile H2S was detected in the headspace of cultures in the absence or presence of Hg2+, and it is suggested that a new mechanism of Hg tolerance, based on the production of non-volatile thiol species, may have
potential for decontamination of solutions containing Hg2+ without production of toxic volatile H2S. 相似文献
14.
Background
Differentiating Dictyostelium discoideum amoebae respond upon cAMP-stimulation with an increase in the cytosolic free Ca2+ concentration ([Ca2+]i) that is composed of liberation of stored Ca2+ and extracellular Ca2+-influx. In this study we investigated whether intracellular cAMP is involved in the control of [Ca2+]i. 相似文献15.
Makoto Fujisawa Yuko Wada Takahiro Tsuchiya Masahiro Ito 《Archives of microbiology》2009,191(8):649-657
16.
Complex signal transduction pathways underlie the myriad plant responses to attack by pathogens. Ca2+ is a universal second messenger in eukaryotes that modulates various signal transduction pathways through stimulus-specific
changes in its intracellular concentration. Ca2+-binding proteins such as calmodulin (CaM) detect Ca2+ signals and regulate downstream targets as part of a coordinated cellular response to a given stimulus. Here we report the
characterization of a tomato gene (APR134) encoding a CaM-related protein that is induced in disease-resistant leaves in response to attack by Pseudomonas syringae pv. tomato. We show that suppression of APR134 gene expression in tomato (Solanum lycopersicum), using virus-induced gene silencing (VIGS), compromises the plant’s immune response. We isolated APR134-like genes from Arabidopsis, termed CML42 and CML43, to investigate whether they serve a functionally similar role. Gene expression analysis revealed that CML43 is rapidly induced in disease-resistant Arabidopsis leaves following inoculation with Pseudomonas syringae pv. tomato. Overexpression of CML43 in Arabidopsis accelerated the hypersensitive response. Recombinant APR134, CML42, and CML43 proteins all bind Ca2+ in vitro. Collectively, our data support a role for CML43, and APR134 as important mediators of Ca2+-dependent signals during the plant immune response to bacterial pathogens.
This work was supported by a research grant (WAS) and postgraduate scholarships (DC, SLD) from the Natural Science and Engineering
Research Council of Canada, the National Science Foundation (IBN-0109633; GBM), and the Swedish Research Council (SKE). 相似文献
17.
The pre-steady states of Pseudomonas species lipase inhibitions by p-nitrophenyl-N-substituted carbamates (1–6) are composed of two steps: (1) formation of the non-covalent enzyme–inhibitor complex (E:I) from the inhibitor and the enzyme
and (2) formation of the tetrahedral enzyme–inhibitor adduct (E–I) from the E:I complex. From a stopped-flow apparatus, the
dissociation constant for the E:I complex, KS, and the rate constant for formation of the tetrahedral E–I adduct from the E:I complex, k2 are obtained from the non-linear least-squares of curve fittings of first-order rate constant (kobs) versus inhibition concentration ([I]) plot against kobs=k2+k2[I]/(KS+[I]). Values of pKS, and log k2 are linearly correlated with the σ* values with the ρ* values of −2.0 and 0.36, respectively. Therefore, the E:I complexes are more positive charges than the inhibitors due to
the ρ* value of −2.0. The tetrahedral E–I adducts on the other hand are more negative charges than the E:I complexes due to the
ρ* value of 0.36. Formation of the E:I complex from the inhibitor and the enzyme are further divided into two steps: (1) the
pre-equilibrium protonation of the inhibitor and (2) formation of the E:I complex from the protonated inhibitor and the enzyme. 相似文献
18.
EstA was purified from the supernatant by A. lwoffii 16C-1. Its molecular mass was determined to be 45 kDa, and the optimal activity occurred when the pH level was 8.0 at a temperature
of 37°C. The activation energies for the hydrolysis of p-nitrophenyl butyrate was determined to be 11.25 kcal/mol in the temperature range of 10–37°C. The enzyme was unstable at
temperatures higher than 50°C. The Michaelis constant (K
m
) and V
max for p-nitrophenyl butyrate were 11 μM and 131.6 μM min−1 mg of protein-1, respectively. The enzyme was strongly inhibited by Hg2−, Ca2+, Mg2+, Fe2+, Cu2+, Zn2+, Mn2+, Co2+, ethylemediaminetetraacetic acid (EDTA), phenylmethylsulfonyl fluoride (PMSF), and diisopropyl fluorophosphate (DFP).
Received: 20 August 2001 / Accepted: 20 September 2001 相似文献
19.
Two experiments were performed to determine how application of the cytokinin benzyladenine (BA) influenced flowering in Doritaenopsis and Phalaenopsis orchid clones. In the first experiment, two vegetative orchid clones growing in 15-cm pots were transferred from a 28°C greenhouse
that inhibited flowering to a 23°C greenhouse for flower induction (day 0). A foliar spray (0.2 L m−2) containing BA at 100, 200, or 400 mg L−1 or 25, 50, or 100 mg L−1 each of BA and gibberellins A4 + A7 (BA+GA) was applied on days 0, 7, and 14. Plants treated with BA alone at 200 or 400 mg L−1 had a visible inflorescence 3–9 days earlier and had a mean of 0.7–3.5 more inflorescences and 3–8 more flowers per plant
than nontreated plants. The application of BA+GA had no effect on inflorescence number and total flower number at the rates
tested. In the second experiment, three orchid clones received a single foliar spray of BA at 200 mg L−1 at six time points relative to time of transfer from 29°C to 23°C (−1, 0, +1, +2, +4, or +6 weeks). A separate group of plants
received a BA application at week 0 but was maintained at 29°C. Inflorescence number was greatest in all three orchid clones
when plants were treated with BA 1 week after the temperature transfer. Plants that were sprayed with BA and maintained at
29°C did not initiate inflorescences. The promotion of flowering by the application of BA suggests that cytokinins at least
partially regulate inflorescence initiation of Doritaenopsis and Phalaenopsis, but its promotion is conditional and BA application cannot completely substitute for an inductive low temperature. 相似文献
20.
Whole cells of the purple sulfur bacterium strain 970 exhibit an unusual absorption peak at 963 nm. Its closest relatives,
Thiorhodovibrio (Trv.) winogradskyi DSM6702T and strain 06511 display a bacteriochlorophyll (BChl) a absorption peak at 867 nm that is characteristic for most light-harvesting complexes 1 (LHC1) of proteobacteria. The puf operons encoding the LHC1 and reaction center proteins were amplified, cloned, and sequenced, and for the Trv. winogradskyi, strains show the common pufBALMC gene arrangement, whereas strain 970 contains a second pufBA copy downstream of pufC. Only pufB
1
A
1
is transcribed, and the corresponding mRNA fragment had an increased stability. Alignments of the deduced protein sequences
showed that the LHC1 polypeptides are closely related to those of Thermochromatium (Tch.) tepidum. A deletion between αHis0 and αTrp+11, thought to be responsible for the redshifted Q
y
absorption in Tch. tepidum, was also detected in strain 970 and Trv. winogradskyi, whereas αLys+12 is replaced by histidine only in strain 970. Based on our structural modeling, the side chain of this αHis is predicted to
be in close proximity to the BChl a, suggesting that it exerts a modulating effect on the spectral properties of the highly unusual LHC1 complex of strain 970. 相似文献